The present invention relates generally to tools for use in dispensing plastic fasteners and more particularly to needles which are used in such tools.
Plastic fasteners are widely used in commerce to attach tags or other items to articles in a manner which minimizes the risk of inadvertent detachment therefrom. One type of plastic fastener is manufactured in the form of fastener stock comprising a pair of continuously connected, elongated side members which are interconnected by a plurality of thin transverse cross links. Typically, one side member comprises a plurality of end-bars or T-bars joined together by severable connectors. The fastener stock is usually produced by molding or stamping from flexible plastic materials, such as nylon, polyethylene, and polypropylene. Additional information pertaining to fastener stock may be obtained from the following commonly assigned U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 4,955,475, issued Sep. 11, 1990; U.S. Pat. No. 4,456,161, issued Jun. 26, 1984; U.S. Pat. No. 4,121,487, issued Oct. 24, 1978; and U.S. Pat. No. 3,103,666, issued Sep. 17, 1963.
The above-described fastener stock is typically loaded into a dispensing tool, often referred to as a "tagger gun." A tagger gun normally includes a hollow needle having a longitudinal slot extending over its length. The fastener stock is inserted into the tagger gun behind the needle. Upon actuation of a trigger mechanism in the gun, an individual fastener is separated from the fastener stock and is inserted into the desired article of commerce through the needle.
In U.S. Pat. No. 4,273,279, which is incorporated herein by reference, a typical needle having a single part construction is described. The needle includes a shank or "stem" portion which has a relatively sharp tip to permit penetration into the article to be attached and an integrally formed substantially cylindrical base portion. The shank portion is hollow to permit the T-bar end of the fastener to pass therethrough and has a longitudinal slot to permit the filament of the fastener to extend therefrom as the T-bar end moves through the needle. The base portion includes a central bore with an inner diameter equal to the inner diameter of the hollow shank. The base portion also has a longitudinal slot aligned with the slot in the shank. The needle is made by machining the shank portion and the base portion from a single piece of metal. As can readily be appreciated, however, machining metal into a desired shape can be a rather arduous and time-consuming task which allows little margin for error.
Also disclosed in U.S. Pat. No. 4,273,279 is a needle assembly having a conventional two part structure. The needle assembly includes a shank portion stamped from a piece of a steel and a base portion which is formed of plastic and is molded around the shank portion. One disadvantage with this type of needle, however, is that the molding process is rather expensive, accounting for an overwhelming percentage of the total cost of manufacturing the needles.
Because needles used in tagger guns tend to break frequently and require replacement, they are typically removably mounted in an opening formed in the front end or "nose" of the tagger gun and are releasably secured therein by means of a locking mechanism in the tagger gun.
For example, as shown in FIGS. 21 and 22 of U.S. Pat. No. 4,456,161, the needle locking mechanism includes a locking pin, which engages a corresponding recessed area formed in the needle. The locking pin is also provided with a cut-out slot which provides a passageway for insertion and removal of the needle. The locking pin is biased in its locking position by means of a spring mounted in the tagger gun. When the locking pin is pushed towards the spring to compress it, the slot on the locking pin aligns with the needle to free it for removal. Preferably, that portion of the locking pin engaging the recessed area of the needle in locking position is rectangular or square in cross-section.
Unfortunately, the above-described needle locking mechanism suffers from certain disadvantages. For example, the needle may be inserted into the opening in the tagger gun in any one of an infinite number of angular orientations. An inherent problem with this mounting procedure is that it is not intuitively obvious or readily apparent as to what angular orientation is correct. If the angular orientation of the needle is incorrect, the locking pin will not properly engage the recessed area in the needle, frequently resulting in needle breakage or in the jamming of the needle in the tagger gun, or in an ineffective locking of the needle. Moreover, one or more components of the locking mechanism may break or require replacement after repeated or prolonged use.
Another patent of interest to the present invention is the commonly assigned U.S. Pat. No. 4,998,661, issued Mar. 12, 1991 and incorporated herein by reference. In this patent, a needle assembly adapted for removable mounting on the front end of a tagger gun is disclosed. The needle assembly comprises a needle encased in a holder which may be easily secured to and removed from the front end of the tool, the holder defining in conjunction with the remainder of the tool at least a major portion of the feed track. In a preferred construction of the needle assembly, the needle is a hollow slotted metal structure and the holder is comprised of plastic which is injection molded around the needle.
In U.S. Pat. No. 4,877,172 there is described and illustrated in FIG. 4 the use of a tapered needle locking screw for locking an inserted needle in place. Although the needle locking screw provides a secure, snug engagement of an inserted needle, it still requires precise alignment of the needle before locking.